Not sure if anyone is still having this issue. I had the same problem while testing and it was the permissions for users on the folder the backups are in. You have to make sure that the Network Service/Administrators/Specific Users have write access to the folder the backups are in. See below.

For anyone who may be experiencing this issue, I've found a resolution. I can't guarantee this will fix your problem, but it worked for me. First, some background--we're working on migrating a 10.4 instance (on Windows) to a new 2018.3 instance (also on Windows). Everything looked good until we tried to restore our old content to the new one. That's when we ran into these problems. I tried many things, but eventually found the following knowledge base article: https://kb.tableau.com/articles/issue/error-tableau-server-initialization-failed-in-configuration-and-initialization-win… The description is not exactly like my issue, but I tried it anyway. After explicitly setting the permissions for my Run As service account, I was able to perform the restore. I should note that, before finding this, I had tried giving the account temporary local admin privileges, but that did not work. For whatever reason, Windows is being difficult and requires that these rights be granted explicitly to the Run As account. I should also note that I my successful restore was executed without the user being in the local admin group.

If you do not see the Security tab and you have admin rights on your computer then open "regedit", go to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer, and set the "NoSecurityTab" to zero:

We upgraded our prod deployment over the w/e to 2018.3 and ran into several issues with the restore, that we for whatever reason hadn't encountered on dev during testing.

Maybe this will help others, so I post here.

Issue 1:

The tsbak file needs to have security allotted to "Network Service". We have no idea what this is about and how this account gets automatically added in some tsbak files and some it doesn't. We were logged in with full admin rights as the runas user and we kept getting "access denied" and the restore would fail right away. But "Network Service" is def needed. Perform a Full Backup and Restore of Tableau Server - Tableau

Issue 2:

There was something confused internally that caused the resotre to keep failing, upon looking in the logs is was trying to access port 8060 of the internal db, but the db wasn't up and therefore the connection was refused. We never got to the bottom of this one, it was a security related thing, instead we did a full obliterate and started over. One thought is when we were setting up the coordinate service ensemble, we went too fast (because it was scripted), and the coordination service got uncoordinated. Per the instructions, you need "several minutes" of wait time to ensure all is setup properly. Deploy a Coordination Service Ensemble - Tableau

Its been a while. I do remember reaching out to Tableau Support and Tableau Sales Consultant's but they were not of any help simply because no one could figure out what was happening, ended up delaying the overall upgrade plan. If the below is of any help to you, here it is ..

So I had mentioned that I tried 2018.2.1 first on our Tableau Sandbox server, eventually our Sandbox OS was re-imaged from 2012 R2 Standard to 2012 R2 Enterprise because of additional RAM support. Once I had the re-imaged server, I freshly installed 2012.2.1 Tableau Server from scratch ( remember everything was wiped out due to re-image, so no previous installation files or configuration existed ) and configured to match similar to what we had before.

I think when I proceeded to do the restore the Prod backup, I succeeded this time.

Something with the previous installation was messing with this and I could not figure that out, wasted hours though. I see few more responses to this thread from when I had seen last, not sure if you went through them all. Good luck. Let us know what you ended up doing, if any different then it could be useful next time.

I have experienced the same issue with 2019.1.4, the restore was working after clean up the log files.

tsm maintenance cleanup -a

Also, please verify if there any .tsbak file on the E:\Tableau\Tableau Server\data\tabsvc\files\backups folder ? If there any failure during the restore, then there would be a tsbak file created under this location. Please remove them too.

Most of time I experience one or the other problem in restoring the backup and few cases opened with Tableau but I manage to fix them before I hear back from Tableau support.